1. Field of the Invention
The present invention relates to a locked phase active power current control circuit, and more particularly to a control circuit which is effective in maintaining the brightness of the light used as LCD background lighting source.
2. Description of the Prior Art
FIGS. 1A through 1C are flow charts illustrating conventional load current feedback control schemes. A DC signal provided by a DC source 11 is converted into a square wave signal by an electronic switch 12 for a driving transformer 13 to operate a load 4, and a current detecting unit 14 is employed to detect the current signal from the electronic switch 12 (FIG. 1A), the driving transformer 13 (FIG. 1B) or the load 4 (FIG. 1C) so as to feed the signal back to a square wave controller 15 in order to set the operating frequency of the electronic switch 12.
Indeed, it is effective using the aforesaid control means to attain the aim of the feedback control, but there remain the following problems:
1. The load current composed of IR, IL and IC will vary simultaneously with variation of the load, causing difficulties for control and affecting the effectiveness of the feedback.
2. If the above control means is applied to control the LCD background lighting, the brightness of the background light will be uneven.
Due to these defects in the prior art, an improvement is urgently required.
The inventor of the present invention has plunged into this matter for years in order to alleviate these defects and has finally succeeded in coming up with the present invention.